Rocoteh: I've been giving the Marine issue a little thought; I don't know if raising the price will stop the AI from building them, they are pretty expensive even now but that sure doesn't stop them! Assuming you want the national infantry units to be the primary force I have a few ideas:
Since you kept amphibious capability for all infantry units, then remove Marine build ability altogether except for US Marines. Allow nations to have a certain number of Marine units to start, but not be able to build any more after that,through tech or resource non-availability. For nations like UK, Japan, and perhaps Italy,etc.; make use of some of those wonders you are putting in to keep cities from being razed, and give them each one wonder that auto-produces UK Commandos, Japan SNLF, etc. That way you can fix the rate at which new Marine types come into play...it should be fairly long between units. Say 1 per 8 turns for Japan, 1 in 10-12 for UK and Italy? I think the Islands are takeable without Marines, they just make it a lot more feasible. I want to see them in, but we need to get a handle on the AI building them;in my Turkey game the Soviets are using Marines and Paratroopers almost exclusively now.
Oh, and maybe limit the paratroopers to a few starting units;they were not fielded in large numbers except by US and Germany maybe,and they were hard to replace. Limiting them to the starting units would make them more precious, and would stop the AI from over-building them. You could use another wonder for Germany & US auto-production, but I realize that is a lot of work and maybe not worth it to you.
Last Turkey report, I am giving it up for now since I want to try Japan. They were viable, but I was getting frustrated with my weak offensive units. For the playable minor nations like Turkey and Argentina, please consider a FEW possible upgrades down the road. They don't have to match the majors, just give us something to look forward to if we survive that long!
Week 33,1940- Axis make peace with Soviets, Allies declare war on Soviets! ... weird.
Week 35- I take Crete, narrowly. I wanted the gems.

I would have beaten the Greeks eventually, it was just proving more costly then I expected,
Week 38- Sarmi liberated by UK. Osaka, Ikita to US. Two pronged invasion of Japanese homeland!
I stopped it there, am trying Japan now. I want to see how long it takes the Axis to get into war with Soviets without a silly Japan geting them embroiled early. I like the fact that I lack Oil and Rubber to start. I just realized I have only two ground units with worthwhile attack, and they are both regulars...this is going to get sticky. I neglected to buy Oil & Rubber from my axis 'partners', and they now won't trade with me on turn 2.

Something about my being too poor to afford it.

I am heading for the Dutch Islands! I took Guam before I saved it during Week 37,but it is going to cost me a transport. More later.
Oh, and the changes to the Axis minors seemed to work fine except for the Finns. I don't think you need to worry about the HMGs; they are beatable, but they do increase the costs to attack. I watched the Soviet marines pouniding on the HMGs in Romania, and they won some and lost a few more; pretty good exchange. Also I think the Wonders being in the cities makes the AI fight for them more: Germany & Soviets were going at it something fierce trying to take those cities. The Germans push on Odessa & Lwow had the side benefit of being protection for the axis minors.